The present invention relates to air handling units, and particularly relates to air handling units used in data center cooling.
Data centers present unique and challenging thermal management concerns. As computing power density has continued to increase, and as the world's desire for data has continued to grow, the infrastructure that handles the storage and access to electronic data has increasingly been concentrated in dedicated data centers. Such data centers typically consist of large rooms or buildings housing electronics racks filled with data servers and associated equipment used to provide data access for computer users distributed around the world. These data centers consume tremendous amounts of electrical power, most of which is dissipated as heat by the electronics housed within the electronics racks. The electronic components themselves are prone to failure at elevated temperatures, and the proper regulation of the temperature of the components by managing the removal of this large quantity of generated heat is consequently of great concern.
This thermal management challenge is quite different from the challenges associated with the thermal management of conditioned spaces for human comfort, as may be found in buildings or spaces of similar size, such as office building and the like. In buildings and spaces where human occupancy is relatively high, emphasis is generally placed on providing adequate ventilation air in order to replenish oxygen, remove carbon dioxide, and in general avoid the accumulation of “stale” air. In contrast, data centers tend to have relatively low human occupancy but a substantially greater amount of heat being generated. Temperature and humidity levels are of greater concern to data center operators, and rather stringent industry standards for these have been developed. The traditional solution to these challenges has been to minimize the rate of air replacement within the data center, and to instead recirculate the air within the data center while removing the accumulated heat by transferring that heat to a cooling circuit. Such a cooling circuit typically uses a coolant such as refrigerant or chilled water to remove the heat from the air being circulated inside the data center, after which the coolant is routed to an external location where the heat is transferred to the environment.
While such systems function well for their intended purpose, they do have certain drawbacks. The substantial quantity of heat must be transferred at least twice—first from the internal air to the coolant, and then again from the coolant to the ambient air—which creates inherent inefficiencies. When chilled water is used, the heat is often transferred a third time, with an intermediate transfer of the heat from the chilled water to a separate refrigerant loop. All of these additional transfers of heat reduce the amount of time that such a cooling system can be operated without a power-consuming mechanical system, such as a vapor-compression refrigeration system, while still ensuring that the temperature of the coolant is both sufficiently below the desired internal space temperature and sufficiently above the ambient air temperature so that the desired rate of heat removal is achieved.